Quick answer? It’s all about competing strengths of attraction between ions, between ions and water molecules, between water molecules themselves …
Key points …
- the anions(-) and cations(+) are scattered randomly throughout the water and behave independently of each other
- water molecules are polar because oxygen atoms are more electronegative than hydrogen atoms (oxygen attracts the electrons in the covalent bond more strongly)
Solubilities of common ions ( you need to learn this!)
| soluble | insoluble |
| all nitrates | |
| all chlorides | except for AgCl and PbCl2 |
| most sulphates | except for BaSO4, PbSO4 and SrSO4 |
| all carbonates, except Group 1 and ammonium carbonates | |
| all Group 1 and ammonium salts | |
| Cu(OH)2, Fe(OH)2, Fe(OH)3 |